Yeah, at the time, the thought of needing more than four billion internet addresses probably seemed a bit ludicrous when it was still mostly just government and university mainframes connecting. That number must have seemed like a nearly never-ending well, especially seeing how generously it was initially carved up into massive blocks. Some of the earliest corporations and universities to receive allocations still have a relatively ridiculous number of Class A blocks allocated addresses (16+ million).
We'd probably still have plenty of addresses were those initial blocks handed out a bit more judiciously, but again, part of that was done, if I understand correctly, for simplicity of routing. It's easy to criticize with the hindsight of today's hardware and needs, but those early computers were incredibly restrained on memory and CPU speeds. Even a 64-bit address would have been seen as doubling memory requirements of routing hardware for no good reason.